1. Field of the Invention
The present invention relates to a phase shifting mask (PSM) for manufacturing a semiconductor device and a method of fabricating the same, and more particularly, to a phase shifting mask (PSM) using an assistant pattern and a method of fabricating the same.
2. Description of the Related Art
Resolution enhancement techniques are employed in manufacturing semiconductor devices using optical lithography at around the resolution limit. Such resolution enhancement techniques include off-axis illumination and use of a phase shifting mask (PSM), for example especially a half-tone PSM.
The resolution of a specific target pattern can be increased by using a resolution enhancement technique. However, the resolution of a pattern having a different size and distribution from the target pattern is lowered according to a phenomenon referred to in the art as the optical proximity effect. An optical lithography technique for reducing the defects is referred to as optical proximity correction, and various optical proximity correction techniques have been used.
Examples of the defects caused by the optical proximity effect include an increase in bias caused by a decrease in a critical dimension (CD) of an independent pattern and a decrease in depth of focus. When forming a device pattern using optical lithography, the problems can be solved by using a mask for forming a scattering bar or an assistant pattern around the device pattern for reducing the optical proximity effect to cause the device pattern to act as a pattern grouped with the independent pattern without being individually resolved, and by using a mask for forming an assistant pattern around the device pattern. In general, since the assistant pattern must be formed far smaller than the device pattern, it is difficult to manufacture such a mask. It is also difficult to apply the assistant pattern to a small device pattern.
In particular, in the development of a PSM, it becomes important to precisely control the phase formed in the transmitting portion of a mask. However, when forming a small assistant pattern, it is not easy to precisely inspect whether the assistant pattern has formed properly.